Admixtures for filling natural and artificial subterranean voids

ABSTRACT

THE BACK FILLING OF NATURAL AND ARITFICIAL SUBTERRANEAN VOIDS FOR PURPOSES OF SURFACE SUBSIDENCE CONTROL AND ACID ENTRAINED WATER DRAINAGE CONTROL COMING FROM SUCH VOIDS WITH A FLUID FORMED ADMIXTURE OF A CEMENTITIOUS NATURE WHICH SOLIDIFIES UPON SETTING IN THE VOID, THE RATE OF SOLIDIFICATION CONTROLLED BY THE AMOUNT OF HYDRAULIC CEMENT OR SILICIC ACID ADDED TO THE ADMIXTURE. IN THE SITUATION WHERE THE GROUT IS EMPLOYED ALSO FOR CONTROL OF ACID ENTRAINED WATER DRAINAGE, INGREDIENTS ARE ADDED TO REDUCE THE ACID CONTENT TO A BY-PRODUCT WHICH IS PLACED IN COLLOIDAL SUSPENSION IN A GELATINOUS MATERIAL IN THE ADMIXTURE DUE TO FERMENTATION OF AN ACTIVATING AGENT WITH A FERMENTING AGENT OF VEGETABLE MATERIAL AND ELIMINATE FURTHER FORMATION OF ACID FROM SUBTERRANEAN POTENTIALLY FORMABLE ACID BEARING STRATA TO THEREBY RE-ESTABLISH THE WATER TABLE AS WELL AS PROVIDING SAFE PLATABLE WATER. ADMIXTURES CONTAINING NATURAL ELEMENTS ARE PROVIDED WHICH FORM A HYDRATING SUPPORTING MASS. WHEN THE MASS SOLIDIFIES, IT POSSESSES A STRAIGHT POROUS NATURE. IN THE CASE OF ADMIXTURES POSSESSING A FERMENTATION ACTION, THERE IS A LEAVENING ACTION CAUSING THE MASS WHEN PLACED IN A SUBTERRANEAN VOID, TO BLOAT AND BE EXPANSIVE IN NATURE TO COMPLETELY FILL THE AREA OF THE VOID.

3,799,787 Patented Mar. 26, 1974 "Ice material to be supplied to thevoid area to bring about 3,799,787 solidification upon setting toprovide for surface support ADMIXTURES FOR FILLING NATURAL ANDARTIFICIAL SUBTERRANEAN VOIDS William A. Davis, Kittanning, Pa.,assignor to Michael L. Vongrey, Jr., Kittanning, Pa.

No Drawing. Original application Aug. 19, 1969, Ser. No. 851,457.Divided and this application Oct. 25, 1972, Ser. No. 300,870

Int. Cl. E02d 3/12; C09]: 3/00 US. Cl. 106-287 SS 17 Claims ABSTRACT OFTHE DISCLOSURE The back filling of natural and artificial subterraneanvoids for purposes of surface subsidence control and acid entrainedwater drainage control coming from such voids with a fluid formedadmixture of a cementitious nature which solidifies upon setting in thevoid, the rate of solidification controlled by the amount of hydrauliccement or silicic acid added to the admixture. In the situation wherethe grout is employed also for control of acid entrained water drainage,ingredients are added to reduce the acid content to a by-product whichis placed in colloidal suspension in a gelatinous material in theadmixture due to fermentation of an activating agent with a fermentingagent of vegetable material and eliminate further formation of acid fromsubterranean potentially formable acid bearing strata to therebyre-establish the water table as well as providing safe palatable water.

Admixtures containing natural elements are provided which form ahydrating supporting mass. When the mass solidifies, it possesses astraight porous nature.

In the case of admixtures possessing a fermentation action, there is aleavening action causing the mass when placed in a subterranean void, tobloat and be expansive in nature to completely fill the area of thevoid.

CROSS REFERENCE TO RELATED APPLICATION This is a divisional of patentapplication Ser. No. 851,- 457 filed Aug. 19, 1969 in the name ofWilliam A. Davis.

BACKGROUND OF THE INVENTION This invention relates to hydraulic andearth engineering and more particularly to earth control andcompositions used in earth control programs. (61-35), (252-85-+),(299-11). (l0685+).

Many substances and mixtures have been conceived in the past concerningthe filling of natural or artificial voids found in the earths crust orin the subterranean areas below the earths surface, whether these voidsconsist of natural fissures or cavities, or abandoned mined-out areas,or the stabilization of soil masses beneath the surface of the earthupon which building structures have been built or intended to be builtin the future. Included in these are the teachings of the followingpatents of interest:

October 6, 1903.

September 27, 1921. January 17, 1922.

August 25, 1931.

October 13, 1931. September 2, 1941 (til-36). July 17, 1951 (61-36).March 4, 1952 (106-90). February a, 1953 (01-35).

3 April 10, 1962 (166-29).

93 September 12, 1967 (61-39).

Armentrout 3, 028, 91

Row 3, 340, 6

Reprints of papers presented before the Second Symposium on Coal MineDrainage Research; Mellon Institute, May 14, 15, 1968, Pittsburgh, Pa.

These patents involve the use of various elements forming a compositionor mixture of a cementitious nature some'of which may containconventional hydraulic cement together with various types of aggregatesas a binding and prevent subsidence. In some cases, an element is addedto the admixture to bring about an expansive nature to the entiremixture which, upon solidifying, expands to fill completely the voidunder consideration, particularly where fine subterranean fissures andcrevices are involved. The main intent is to provide a rigid mass forback-filling of natural and artificial voids. In another case, theprevention of subterranean water flow into a mined-out cavity iscontemplated but it has been known for many years past that it is nextto impossible to stop or prevent the flow of subterranean waters withthe result that the only practical approach is to permit suchsubterranean water to flow but at the same time divert their courses andcheck and control for acid entrainment thereof.

A representative example of the above patents is that to Poulter2,627,169 wherein the method is provided for solidifying porous massesof earth or masonry and concrete by combining portland cement insuspension with a finely divided material containing sufiicient acidiccolloidal silica to retard gelation of the cement, and an oleaginousmaterial, the cement and the material placed in suspension and renderthe resultant slurry highly plastic and flowable and capable ofpenetration. However, the problem of filling large voids, such as amined-out area, is not contemplated or readily solved particularly whereneutralizing of acid entrained mine drainage is involved and there-establishment of the water table to provide for a palatable watersupply.

It is the main intent herein to provide highly inexpensive cementitioustype compositions or grouts for use in connection with surfacesubsidence control as well as provide in such grouts, where necessary,ingredients which bring about an expansive nature to the grout forfoamin or bloating upon solidification the entire grout mass after thesame has been poured into a natural or artificial void. In this mannerthe subterranean water flow may be diverted and naturally filteredpreventing the formation of acid entrained water flow to insurere-establishment and stabilization of the subterranean water table.

SUMMARY OF THE INVENTION This invention relates to the use ofinexpensive fluid compositions or grouts having a cementitious naturewhich are supplied by means of pumping into underground natural orartificial (man-made) voids within the earth's crust to be allowed tothereafter harden, the rate of solidification dependent upon theparticular situation and requirements. Such natural voids in the earth'scrust include subterranean fissures, crevices, caverns, fractures,water-bearing strata, etc. or artificial voids produced by mining, suchas abandoned coal mines and surface mined or stripped areas, commonlyreferred to as open pit mines, which have been abandoned and are to beor should be back-filled for returning the mined area back to a useableform for use by man.

It is the principal object of this invention to back-fill subterraneanmined-out areas with a highly inexpensive fluid grout which hardens intoa solid mass upon aging. Such a composition is used to fill natural orartificial voids within the earths crust as subsidence control programwhere potential subsidence exists particularly where buildings arepresent or are to be built on the surface of the earth. Due to the manynow abandoned mined-out areas existing in many parts of the country,such as, the Appalachian Lowlands, there is more than ever an urgentneed for subsidence control. These mined-out areas having now existedfor a number of years, in many cases well over 50 years, and nowsubsidence of the earths crust or surface is being reported in many suchareas. The

old supports in these abandoned mines have now subsided due to age andthe support of the subterranean area between the mined-out area and thesurface soon begins to subside due to lack of proper support. Thisbecomes a particular problem when there are present on the surface ofthe ground, homes or buildings which, of course, depend on goodsubterranean support. Upon proper analyzing of surface and subterraneanconditions, the fluid compositions or grouts of this invention may bepumped into the mined-out areas to provide and insure proper surfacesupport for building structures.

Another principal and very important object of this invention is controlof acid entrained mine or subterranean water. The pollution of watershas become a major concern today since it contaminates our streams,destroys aquatic life, and poisons waterfowl and other wildlifecreatures. The resultant effect is the spoiling of the landscape withthe end effect of degrading the environment in which we live.

The main objective here is principally in connection with acid entrainedmine drainage being constantly produced from active and abandoned mines.When these subterranean cavities are produced by man, certain elementsare exposed unnaturally to the atmospheric environment and as aconsequence there is produced highly contaminating acids, such assulfuric acid which is carried away by subterranean water. Thesecavities also disturb the subterranean water table by providing a fiowpath different from that which previously existed naturally. As aresult, the water table is dissipated or contaminated or both. By thesame token, the acid entrained drainage from mined-out areas seeks theeasiest courses which are the mine exits and contaminate nearby streamsand rivers.

By supplying a medium of a suitable admixture, it is the principalpurpose herein to return the King of Acids (sulfuric acid) to natnr e1smult, the man-ma mine 613W by neutralizing the acid entrained drainageprecipitating from the mine, forming a grout with this drainage, if ofsuflicient magnitude, and pumping the grout into the mined-out cavity toseal the cavity with the grout. The grout, being of natural elements,.is permeable to permit subterranean waters to filter and penetrateslowly through the grout when solidified. As such, the grout functionsto seal potential acid forming subterranean strata from an airenvironment but at the same time provides a natural filtering system toprovide for re-establishment and stabilization of the water table andchanges such underground water to fresh palatable water useful tomankind.

Many attempts have been made to eliminate the flow of acid entraineddrainage from mined-out cavities. One such old method is by sealing offthe mine entrances. However, it is impossible to stop the course ofnature, and the fundamental flow of subterranean waters. As a result,subterranean waters will build up a pressure head and seek escape fromunderground by means of the path of least resistance. This may be aroundthe edges of a sealed mine entrance or through fissures in the groundleading close to the surface which proved a convenient flow path after asufficient pressure head has been built up.

Another method for sealing mines has been the employment of pumpedconcrete under pressure through small diameter boreholes. This method,as is demonstrated by the prior art, has been used successfully in thestabilization of building foundations. However, as can be expected theuse of concrete mixtures is a highly expensive proposition and for thisreason, has only been used for foundation stabilization rather than thebackfilling of mined-out cavities.

This sulfuric acid can be reduced by a lime slurry to produce ferroushydroxide and calcium sulfate together with water.

An acid mine drainage treatment plant utilizing such a neutralizationprocess requires a subsequent oxidation process, usually accomplished bymeans of aeration, in order to reduce the ferrous hydroxide formed intoferric hydroxide. After this process, there follows sludge settling andhandling and, at last, sludge disposal. By providing the properingredients in various forms of inexpensively produced grouts, suchmined-out cavities can be efficiently filled with grout eliminating thenecessity of providing the treatment plant mentioned above, whichinvolves several processes and more expense as to maintenance.

It is the real intent, therefore, in this invention to as best aspossible duplicate nature by attempting to restore the mined-out areainto its original condition before disturbed by man using natural andabundantly found elements in the backfill materials.

One of the present methods being used now to control acid entrainedwater is the building of treatment facilities at stream sites having ahigh degree of acidity and using a separate lime neutralization processwhich increase alkalinity of the water to a point where it will sustainaquatic life. Examples of such treatment facilities can be found in thereprints of papers presented before the Second Symposium on Coal MineDrainage Research, Mellon Institute, May 14, 15, 1968; Pittsburgh, Pa.Such a process is highly expensive particularly when viewed from thenecessity of a multitude of such treatment plants and facilities tocorrect all of the now acid entrained streams and rivers, rendering sucha treatment exorbitant in expense and unattractive for practical use.Not only is a capital expenditure involved but also the expense ofcontinual maintenance and operation due to the fact that in a short timethe lime application becomes ineffectual because widely dissipated inthe acid entrained stream over a period of time after the lime has beenadded to the stream. Also continual additions of lime are required,based, of course, on the size of the acid control plant, and the degreeof acid content in the steam being controlled.

Another method for controlling acid entrained mine water drainage is theair sealing off the mine or, by more recent theory, sealing off the mineand maintaining an inert atmosphere in the mine. The basic principleinvolved here is to exclude as much as possible, oxygen from a mine toprevent the oxidation of pyrite in the coal left in the mine andadjacent strata and thus prevent the formation of sulfuric acid.However, it has been found extremely diflicult to seal off mines sincemined-out areas breathe and as a result, it makes it impractical tocompletely seal off a mine air-tight or hold an inert atmosphere in themine. Also, when sealing off the entrance of a mine, the pressure of themine water in many cases is sufficient upon building up to seek its ownpath and exit from the minedout area making it impractical to seal themine with an inert atmosphere.

The only real practical way to prevent the foundation of such acidentrained mine water is to concern ones self with the mined-out area perse and seek to backfill the mined-out area by means of filling a minecavity with fluid cementitious type grouts or diking area of the minewith such grouts to prevent the formation of acid entrained 5 waterscausing such waters to revert again to natural It is well known thatmine acid or sulfuric acid can 7 be neutralized by use of hydrated lime.The use of lime for mine acid control has been used extensively. Thechemistry of such neutralization is as follows:

subterranean courses and as a result stabilize and recover theunderground fresh water supply. To accomplish this, an inexpensive fluidgrout may be utilized, as above mentioned, having acid neutralizingproperties to neturalize the presently existing acid entrained mine'water and capable of bloating or expanding to fill the mine cavity andprevent further forming of acid entrained mine water and its flow fromthe mined-out area.

Thus, it is a provision of the present invention to provide a fluidleavening agent entrained composition or grout for backfilling andhydrosealing of a mined-out area or excavation wherein the fluidcomposition becomes solidified within a minimum time of four to eighthours and producing a hydrate creating a filter pack and diverterforsubterranean water and preventing the formation of acid entrained minewater which filtered and diverted water upon reaching surface streams,is useful for human and aquatic life.

Another provision of the present invention is the use at diking to formunderground reservoirs. for, water retention such as in strip mine areasprior to backfillirig w prevent the formation of acid entrained water.Since, strip mining is generally done in adjacent contour stripsfcontourdiking is performed to hold and maintain the water table that originallyexisted.

The particular constituents in the fluid composition or grout to beselected for subsidence and acid entrained water drainage controldepends upon the subterranean environmental conditions at the sitewherein such a program is to be carried out.

In subsidence control, the following procedure is generally followed indetermining where potential as well as actual subsidence exists,particularly where a building structure on the surface has been enlargeddue to potential subsidence, and the measures to be taken to correct forsuch subsidence including the proper grout to be employed.

First, information must be gathered as to the substrata formations ofthe earth below the existing building structure or a construction site.This information would include the substrata formations down to thecavity or void, such as an abandoned mine, creating the condition ofpotential subsidence.

Secondly, and now assuming an existing building structure is present,information must be obtained concerning the footers of the buildingstructure. This information may be provided from old drawings inconnection with the original construction of the building structure.

Thirdly, depending on the type of building structure, information mustbe obtained as to caissons, pilings, spread footers or floatingfoundations of the building structure so as to prevent destruction tothe building when drilling test holes or bores used to possibly locatethe subterranean void and thereafter pump the grout into the locatedsubterranean void.

Fourth, compression tests should be made of the soil conditions and thesubstrata formations to determine the strength and capability forsurface support.

An accepted engineering practice used to find the load bearing factorper square inch of ground is the employment of a timber approximately /2foot by V: foot in cross section which is placed in a vertical positionon the ground area to be tested and maintained in this position byguides positioned at its base. An exact one ton weight is applied to andmaintained at the top end of the timber to determine the degree ofpenetration of the bottom end of the timber into the ground over aperiod of time, such as, for example, one hour; one day; thirty days;and then sixty days.

Fifth, determination should be made for possible lateral and subjacentmovement of substrata formations to determine the subterranean directionand probable magnitude of a potential subsidence. This is particularlytrue in these situations where the building structure is on the side ofa hill. Potential side hill movement must be determined.

Sixth, from the foregoing information, it will be possible to make adetermination of the balancing factor of subsidence control, that is, inconnection with an existing building it will be possible to make adetermination of the moments of inertia effecting the building, such asthe bending moments of the structure.

Seventh, from this balancing factor, a determination ,can then be madeas to the proper ingredients to be used in the fluid cementitious groutto prevent futuresubsidence.

. 6 In the situation where a building structure is to be built on thesite, consideration must be had as to the final weight of the structurein determining the balancing factor.

Eighth, if an artificial void is involved, such as an abandoned mine,maps showing the details of the mine should be studied as to wheresurface subsidence may possibly occur and at what specific areas, if notthe entire mined-out area, in the mine should be filled with grout toprevent potential subsidence. If a map or drawing of the mine is notavailable, test holes must be drilled to determine, the layout of themine. In determining the layout of the mine, unknown to anyone, a studyof the terrain or topography is made and when considered with knowledgeas to how subterranean geological veins of materials of the earth areformed in direction and magnitude for the particular region involved,such as a coal vein, then a very good determination can be made as thepossible loca; tion and layout of the mine.

Generally with respect to older mined-out areas, once there is knowledgeconcerning the original subterranean coal vein, then the mine layout canbe determined with relative accuracy because these older mines generallyfollow a pattern wherein the main shaft would go in for several hundredfeet to a T intersection, one channel of the T providing the air andfluid drainage channel and the other channel of the T being the mainlead-in to mine proper. The probable layout can be checked by drilling aseries of test holes into the subterranean level of the mined-out area.These sametest holes can be used to pump into the mined-out area, theprepared grout.

Usually, when a mine is involved in a subsidence control program, therealso exists the problem of acid entrained mine water drainage appearingin streams and coming from the mine entrances and natural openingsformed by the drainage coming from the mined-out area. Also, suchdrainage may have contaminated the existing water table in the vicinityof the mined-out area. As mentioned above, the grout of this inventionmay be provided with a highly inexpensive expansion agent to not onlyprovide for subsidence control but also provide for mine acid drainagecontrol by purging the mined-out area with foam forming and expansivegrout to seal off further direct drainage from the mine and prevent theformation of further mine acid as well as creating a forced perviousfiltering system to clear and purify the subterranean water to stabilizeagain the subterranean water table.

A method of a series of diking can be used in large mined-out areas asstrip mine areas to bring about control in acid entrained mine waterdrainage. In the case of strip mine areas, not only can reclamation behad of the stripped area but also by proper contour diking in the stripmine pit areas can re-stabilize and maintain the water table that oncepreviously existed in natural state.

Reference is now made to the ingredients used to make the admixtures ofthis invention.

It is well known that one of the most abundant elements found on theearth is silicon which is found in a natural state in variouscrystalline forms and modifications. Silicon dioxide, SiO which isreferred to as silica occurs frequently in nature in a wide variety offorms such as quartz, sand, flint, etc. and constitutes about A; of theearths crust.

' Silica in suspension is known to have a high adhering or cohesiveaction upon which hydration also may be referred to as a cementitiousaction. A colloidal suspension of silica is also referred to as silicagel and is produced by the reduction of silica by, for example, a strongacid to produce the composition expressed as (SiO (H O), having greatcohesive action. Many believe that silica in suspension'occurring innature on a continuous basis is a primary factor for maintenance of theupper layers of the earth cohesively together. If this did not occurnaturally, the earth would not be as stable as it is now, which is'necesary for mans environment.

Silica in suspension usually occurs very slowly in nature. Naturalsilica in suspension is formed by acids from disintegrating vegetation,such as tannic acid from leaves and tree bark which permeate and seepthrough the ground to lower subterranean layers and strata which uponnatural contact with silica, produces hydrates of silica, giving thesilica the capability of being able to directly combine with water andin forming a hydrate will solidify in a cementitious manner into aporous structural type mass. It is natures own natural chemicalprecipitating action. When this occurs in nature, a cementitiousadmixture is formed having the above mentioned cohesive power on alladjacent solid matter in adjacent strata on layers. In this naturalphenomenon, silica in suspension also has a natural expansive action.

What is done here is to take this natural phenomenon of silica insuspension and duplicate it on a mass scale and increase or acceleratethe natural action artificially so that solidification may occur in amanner of hours.

The basic backfill admixture for subsidence control comprises dry andground culm usually abundantly present in mined-out areas together withwhat I term dry garden cement and water. Garden cement is the familiartop soil found on the very top of the earths surface. The need for topsoil is its mud characteristics as well as its yeast content, as will beseen later. The yeast content of garden cement helps to bring about acohesiveness to the admixture which is maintained after the admixturehas been placed in the area of the void and allowed to solidify. Theculm being the principal element in the admixture, is termed the bulkfiller or carrier.

A sufficient amount of water is added to permit the grout to be pumpedunder high pressure into the void or mined-out area without clogging thepumping facility, the connecting pipe line and the bore or openingprepared to the mine or void to be treated.

Portland cement may be added to this admixture in sufiicient quantitiesto control the period of time of solidification after the grout has beenproperly placed in the void area. An example of use of portland cementis in a final sealing mix used at the entrance of a mine wheresubsidence and surface erosion control level is at a maximum because ofthe weight of surface structures existing or to be built on the surfaceas well as natural environment eroding and penetrating elements.

Since portland cement has the capability of hardening very quickly,rather than varying the quantity of such cement in the admixture, it maybe more convenient to use Carney cement. Carney cement possesses aslower rate of solidification and, thus, is useful where one desiresthat the grout naturally spread and dispersed in a greater area in thevoid or mine area at the point of dispensing the grout into the voidarea. Also Medusa cement may be used together with portland cement, thetwo cements providing for better surface support in subsidence controlsituation. Medusa cement is used with portland cement to prolong theperiod of solidification since Medusa cement will not set for 24 hours.Hydrate lime may also be added to insure initial acid drainage control.

Also sand or gravel may be introduced into the admixture for purposes ofadded strength to the final sealing grout.

Bentonite clay or local ground clay may be used in substitute of gardencement depending upon the availabily of such materials.

In mixing these materials to form the grout, a borrow pit may beprepared which consists of a large pit, the materials from which may beused in the admixture such as the garden cement or clay and culm, ifthese materials are present at the site of the borrow pit. The borrowpit may be prepared on available land near to the area of the void orpoint of introduction of the prepared grout into the void area.

In cases where void areas are close to the surface of the ground wherethere is a building structure, for example within 75 feet of the surfaceof the ground, surface and footer support may be enhanced by usingportland cement and Carney cement together with a bulk filler or carrierin the form of silica loam and garden cement. Where, however, the voidis below 75 feet or involves mined-out cavities, less portland cementmay be used with the elimination of the Carney cement, and culm orbuckwheat shale may be substituted as the bulk carrier to provide forsurface and footer support. These admixtures provide for greater bearingarea for the building structure as compared to the general backfilladmixture first mentioned above and containing culm and garden cement.

The admixture for void areas above 75 feet is quicker setting than theadmixture for void areas below 75 feet and both take care of undergroundwater by dispersing it and causing it to take more stringent andmultiple paths of flow. Subterranean water present under existingbuildings may be, thus, controlled by breaking up its concentration toprovide for a better and increased surface bearing area for a buildingstructure. The greater the concentration of such subterranean water, thelarger the void area to be filled. The admixture being composed ofnatural materials acts as a dispersion bed for dispersing and breakingup such subterranean waters. Upon solidification, it will also act as anatural filter bed while providing for surface support.

The materials employed in these admixtures must be ground or of a sizesmall enough to be pumped through the pump line and the bore holesprepared to void areas. The clay materials in the silica loam andadmixtures above discussed acts as a lubricant for the pumping operationto permit free fiow of the admixture to void area without clogging. Thetype of pumps that may be used are the conventional cement pumps such asthose manufactured by the Koehring Company in Milwaukee, Wis.

In connection with the already mentioned admixtures, a lime slurry mayalso be added to aid in controlling the time of solidification sincehydrate lime will, in a manner, control the water content of theadmixture.

Attention is now directed to admixtures not only useful for bulkbackfilling of void areas but also for control of mine acid drainagewherein there is added a neutralizing agent and also, if need be, aleavening composition to cause the grout to become bloated with manyentrained gas bubbles and thereby creating a natural filter bed for theflowing subterranean waters as well as filling up completely fissuresand cracks or caved-in areas of void areas to be sealed.

As a bulk carrier, again dry ground culm or dry ground clay may be used.As a general backfilling admixture with a neutralizing agent, hydratedlime and sand entrained silica loam may be provided with the bulkcarrier.

{Where a large void area is involved and it is desirable to fillcompletely the entire void area and provide and maintain acid drainagecontrol, with the minimum of expense in regard to the materials to beutilized, soapstone may be used with the bulk carrier and lime slurry.Soapstone is excellent in an acid control program because it can beabundantly found. Doloris clay can be used instead of soapstone.

An admixture for back filling and mine acid control can be providedwhere quick setting of the grout is desirable as well as the formationof a massive filtering and dispersion bed upon solidification. Thisadmixture comprises a large quantity of soapstone, although a selectedamount of the bulk carrier, such as clay or culm, may also be provided,together with hydrated lime, silica loam and portland cement. Sufiicientwater is added to make the prepared grout fiowable by means of pumping.

At best, the preferred mine acid control neutralizing admixturecomprises a bulk carrier such as crushed or ground culm obtained from aborrow pit or mine spoil pile to which is added soapstone, gardencement, a

vegetable flour, silica loam and hydrated lime. In this admixture thesilica loam is prepared for suspension by the flotation action of theyeast abundantly present in the garden cement fermenting with thevegetable flour. Examples of vegetable flour are corncob flour, wildwheat flour or rice flour.

The water for these admixtures may be any water locally available. Themost available and preferable water in the case of a mined-out area isthe mine acid drainage which is collected in the borrow pit andneutralized by the action of the admixture. The soapstone containing alarge amount of iron oxide reacts with the sulfuric acid in the water toform a reddish material comprising sulfates and sulfides of iron whichis held in the colloidal formation of silica and in the formed gasbubbles developed throughout the entire admixture due to thefermentation of the yeast and vegetable flour vehicle. As a result, theadmixture has the property of bloating or expanding, due to theleavening action, to fill the entire void area including caved-in areasat the top of the void cavity and also functions to produce a perviousbed of material upon solidification to filter the subterranean waters,dispersing their flow into a multitude and of divergent paths and,further, sealing off acid forming strata layers in the void cavity fromoxidizing elements of the atmosphere to prevent further formation ofmine acid drainage. This natural filtering and dispersion also providesstabilization and maintenance of the water table which is readilydestroyed in underground and strip mining. Solidification of theadmixture will seal therewithin the potentially acid forming materials,such as found in culm and pyrite, to maintain such materials dormant aswas the case before they were originally disturbed by man and exposed tothe atmosphere and other elements such as magnesium, alumina, Water,etc. which brought about in a natural way the formation of contaminatingelements, such as, sulfuric acid, detrimental and destructive of livingmatter and animal life.

As previously indicated, the principle of diking may be utilized wherethe mined-out area is not to be ent-irely filled because of a matter ofexpense and also subsidence control is necessary only at specificsurface areas or locations. Contour diking may be employed during stripmining operations as each strip is made and completed ready to bebackfilled. In such cases, the admixture may provide mine acid control.A convenient admixture for this purpose is dry ground culm as a bulkcarrier together with garden cement, hydrated lime, vegetable flour,such as corncob flour, and water.

Reference will now be made specifically to compositions by percentweight comprising the foregoing admixtures to illustrate practicalembodiments of the grout that can be utilized for subsidence control,mine acid control, surface and footer support, diking and a finalsealing mix for entrances to voids or mines constantly exposed tonatural environmental elements.

These admixtures serve only as examples, for purposes of clarity, ofgrouts that may be employed in carrying out the objects of thisinvention and are not and cannot be construed to limit the invention toany particular form because each specific natural or artificial voidsituation requires analysis initial to determine the proper admixture.Also, it must be known whether subsidence or mine acid control both isdesired.

Example I Percent Garden cement or bentonite clay 25 Dry ground culm 7510 used and the space requirements of the void area to be filled.Approximately to 5% of vegetable flour may be added for purposes ofimparting to the admixture an enhanced expansive nature caused from theleavening action of yeast in the garden cement and the flour.

Example II The following admixture is best suited for surface subsidencecontrol where stratified layers underground are present, the Medusacement extending the time for solidification in order to permit highpressure pumping action for a period of time to insure that all areas ofthe void, including small or minute fissures and cracks are filled.

The following admixture is best suited for surface and footer supportwithin 75 feet of the surface of the ground.

By percent weight Reeom- Percent mended range a of Composition turevariation Portland cement. 20 12-30 Silica loam 33 20-45 Carney cement-12 5-20 Garden cement 35 20-50 Total As can be seen, the silica loam andgarden cement would be the bulk fillers. Since the void to be filled isclose to the surface of the ground, strong cementitious admixture isprovided with the bulk carrier being preferably of materials commonwithin 75 feet of the surface of the ground. Fissures or voids presentwithin this ground area are normally not of large size as compared tothose of a mined-out cavity or a deep subterranean cavern.

Example IV The following admixture is best suited for surface and footersupport below approximately 75 feet from the surface of the ground infilling of the void areas down to and including old mine workings.

By percent weight Recom- Percent mended range 0 Composition turevariation Portland r-emenf 12 5-20 Hydrated lime 6 3-10 Silica loam 3320-45 Garden ement 20 12-30 Buckwheat shale 29 20-40 Tni'nl 100 The limeincluded is only a small percentage and is added to bring about anyrequired neutralizing of mine acid drainage that may be present at thetime of placement of the grout. Note that the bulk filler here consistsof the shale common to such workings and the silica loam to provide thesilica suspension. The portland cement gives added strength depending onthe surface bearing factor desired, as well as controlling the rate ofsolidification.

As to those admixtures where mine acid control is desirable, thefollowing examples with percent range of variation are given.

12 Example 1X Composition: Amount in pounds Crushed or ground culm (bulkcarrier) 1800 EXAMPLE V Garden cement (activating agent) 300 5 Hydratedlime (direct neutralizer) 150 Soapstone (neutralizing reactionaryreagent) 500 BY Percent wegm Vegetable flour (fermenting agent vehicle)50 Recom- Percent Silica loam 300 mended range admixof Composition turevariation 3100 l oo i l g nau r ig clay or dry ground culm 70 60-?8 Inthose cases where the void opens to the surface or issaidEmmi-siniaan::::::::::::: 22 35 exposed to atmospheric i o a p l fisealing T m 100 admixture may be provided which is weather and erosion Fresistant to surface water and other natural environ- 10 mentalelements, as follows.

EXAMPLE VI By percent weight EXAMPLE X Recom- Percent By percent weightmended range 90 admix- Recom- Percent Composition ture variationmgrrigied range;

8 X- 0 Local ground clay or dry ground culrn 67 50-75 Composition turevariation Soapstone.... 27 -40 Hydrated lime 6 3-10 Dry ground culm 35-45 Dry garden cement 22 15-30 Total 100 25 Portland cement 8 4-25 Sandand gravel 35 20-45 These foregoing examples represent the least expen-100 sive admixtures for combination subsidence and mine acid control.The following example has added thereto portland cement to control therate of solidification as Concrete base here is an a greater quantity ascompared well as produce a fast drying grout. to previous admixtures inorder to provide a greater firmness and hardness upon solidificationand, as a practical EXAMPLE VH manner, provide for improved erosionresistant to surface By percent Weight waters. Also /2% to 5% volume(preferably 1%) of silicic acid may be added to admixture instead ofportland Recom- Percent mended range cement to bring about the necessarydegree of hardness. Composition 3;: g; Ih1s compound is known to bereadily prepared by heating silica in colloidal suspension. i gjgg 40 Aspreviously mentioned, the iron oxide in the admix- Silica loam... as20-45 ture reacts with the sulfuric acid to form a rust colored Pmlmdcement sulphate which is sealed within the admixture upon the Total 100flotation action of the yeast of the garden cement combining with thevegetable flour and, is situated in the sus- For purposes of undergrounddiking and contour dikg i ogthe colloidal 2 i g g fi ing in a strip mineoperation and yet provide for drainage 3 3 Z ii zg e u es gi control andneutralization of the Water table, the best i lslzlerse mug g i a s 1suited admixture is as follows: Ion an F p as suc an glve grou up suchsolidification an expandlng or bloating nature in EXAMPLE 1 order thatcomplete filling of the void area can be ac- B 8mm Wei ht complished. Atthe same time, the solidified grout is pervious to subterranean watersperforming the function of a 25x 3 gg g filtering and dispersion bed.The silica in suspension being admix. withheld in a bonded massduplicates the action of nature Composimn Timon in providing clear anduncontaminated subterranean water grydgroundcutlm 3g gag- 55 supply aswell as restoring and stabilizing the previous 8.1 en roman a Hydratedlime 3 H water table which was destroyed by man 1n disturbing theVegetable flour oomco flour) 2 3 -5 subterranean layers as by mining.

100 In the case of subsidence and mine acid drainage con trol, thenormal procedure for filling such mine cavities is to drill several boreholes into the mine cavity through wlmectlon Wlth the p j fi amlxmfe for1111116 which is dispensed the grout. A locking plug may be proacidcontrol as W s provldmg subslflencei Control, the vided in the boreholes in order to act as a check valve f011WlI1g 1S Pficred y y Qexample 111 Welght- A batch and prevent the grout, due to back pressure,to be forced is prepared in the borrow pit and is approximately 3000 kout of h b h l P P cublc y It Should benoted that there 15 65 In mostmine situations, particularly the older mine approximately 325 p l ofYeast 111 311 acre of g workings, it is generally true that a lot ofcave-ins have gardel} cement w 15 meant here y 8 garden occurred fallingin from the top of the mine cavity tunnel ment is good enriched blacktop soil. However, it is not and continually occurring creating cavitiesextended upalways necessary to use such top soil. Top soils of lesserward from the original mine void toward the surface enrichment may beused. The amount of soil in the admixlevel. The first operation isusually underground diking ture need merely be increased to obtain thenecessary with use of the admixture (Example VIII) above given amount ofyeast to bring about the desired leavening to seal the entrances to themined-out area. Then with action. The type of garden cement to be used,of course, the provision of several bore holes into the entire mine willdepend greatly on its location and proximity to the cavity, admixturemay be supplied to completely fill the area of void to be filled.mined-out area using for example, the admixture of Ex- 13 ample IX.After this has been accomplished, the final sealing admixture of ExampleX can be employed to seal the entrances of the mine, which admixture iserosion resistant to surface drainage and atmospheric environmentalelements.

In the case of contour strip surface mining, the general strip pitmining usually occurs on a varying elevation from a low line levelstarting at the crop line wherein the first cut is made, up to a higherlevel wherein the last cut in the strip mining operation is made. Aseach cut is made, a dike using the admixtures of this invention, such asadmixture VIII, is formed against the lower high wall usually about 10to 16 feet in height in order to prevent the seepage and drainage ofacid mine water which developes upon exposure of the pyrite and othersuch elements to the atmosphere as well as holding back subterraneanwaters, in the manner of a previous levey, and thereby maintaining thewater table that previously existed before commencement of the stripmining operation. After the dike is built, the previous strip pit areamay be filled by the materials obtained by the next adjacent contourstrip mining cut. This process of diking and refilling of the adjacentstrip mining cut is continued until completion of the mining operation.

Upon final contouring of the area of the strip mining operation, whichis now generally required by law, surface diversion trenches may beprovided on the surface of every other previously strip mining cut inorder to divert surface water quickly away from the mined area andprevent the seepage and penetration of disintegrated vegetable mattersuch as leaves, bark and other vegetation to permeate the strip minearea. As a matter of assurance, the diversion of surface watereliminates the further possible contamination of subterranean water,which after contaminated, may sink into the relocated strip mine fill.

I claim:

1. An admixture for filling natural and artificial subterranean voidssolidifying into a hardened mass consisting of a bulk carrier and fillercomprising crushed dry culm 60%-wt.85%-wt. and a lubricant agent 14%-wt.35 %-wt. comprising yeast entrained top soil together with water to forma slurry.

2. The admixture of claim 1 characterized by bentonite day as alubricant agent in lieu of yeast entrained top soil.

3. The admixture of claim 1 characterized by the addition of portlandcement to control the rate of solidification of the admixture when beingplaced into the subterranean void.

4. The admixture of claim 1 characterized by the addition of Carneycement to control the rate of solidification of the admixture when beingplaced into the subterranean void.

5. An admixture for filling natural and artificially formed subterraneanvoids substantially close to the surface of the earth solidifying into ahardened mass to provide for greater surface support and footer supportfor existing building structures consisting of a bulk filler comprisingsilica in colloidal suspension produced from hydrous formation of silicaloam 20%-wt.-45%-wt. and yeast entrained natural soil 20%-wt.50%-wt.

6. The admixture of claim 5 characterized by the addition of portlandcement l2%-wt.-30%-wt. to control the rate of hydration and give addedstrength to the admixture on solidification.

7. The admixture of claim 6 characterized by the addition of Medusacement 5%-wt.-20%-wt. to control the rate of hydration of the admixturewhen being placed into the subterranean void.

8. The admixture of claim 6 characterized by the addition of Carneycement 5%wt.20%- wt. to control the rate of hydration and give addedstrength to the admixture on solidification.

9. An admixture for filling natural and artificially formed subterraneanvoids more than approximately seventy-five feet below the surface of theearth solidifying into a hardened mass to provide for greater surfacesupport and footer support for existing building structures consistingof a bulk filler 20%-wt.40%-wt. selected from the group consisting ofdry ground culm, buckwheat shale, and bentonite clay, and silica incolloidal suspension produced from hydrous formation of silica loam20%-wt.- 45 %-wt. and yeast entrained natural soil l2%-wt.-30%- wt. v

10. The admixture of claim 9 characterized by the addition of aneutralizing agent 3%-wt.-10%-wt. in the form of a hydrated lime slurryto effectively neutralize the presence of any acid entrainedsubterranean drainage.

11. The admixture of claim 10 characterized by the addition of aneutralizing agent in the form of a hydrated lime slurry to effectivelyneutralize the presence of any acid entrained subterranean drainage.

12. An admixture for filling natural and artificially formedsubterranean voids solidifying into a hardened mass and neutralizing ofand preventing further formation of subterranean acid drainagecomprising a bulk filler 30%-wt.80%-wt. selected from the group of drycrushed culm, bentonite clay and soapstone, a hydrated lime slurry3%-wt.-10%-wt. and silica loam 15%-wt.-35%-wt.

13. The admixture of claim 12 characterized by the addition of portlandcement 5%-wt.-20%-wt. to control the rate of hydration of the admixturewhen being placed into the subterranean void.

14. In a cementitious type admixture for filling natural andartificially formed subterranean voids hydrating into a hardened massand neutralizing of and preventing further formation of subterraneanacid drainage, the com bination of the following hydratable ingredients:a bulk carrier and filler comprising crushed dry culm, an activatingagent comprising conventional yeast entrained natural soil, a fermentingagent comprising vegetable flour, a gelatinous agent comprising silicaloam, an acid neutralizing reactionary reagent comprising a metallicoxide.

15. In the composition of claim 14, the inclusion of portland cement tocontrol the rate of hydration.

16. In the composition of claim 14, iron oxide in the form of soapstonecomprising the acid reactionary reagent.

17. In the composition of claim 14, the inclusion of one or more ofcorncob flour, wild wheat flour or rice flour comprising the fermentingagent.

References Cited UNITED STATES PATENTS 2,158,025 5/1929 Huist 106287 SS2,310,652 2/1943 Peter 71--24' OTHER REFERENCES Chem. Abst. 62:15, 956p(1965).

THEODORE MORRIS, Primary Examiner US. Cl. X.R. 10690; 6136 .WIAu-m.

